Extinction in Subdivided Habitats

Abstract: The effect of the spatial structure of populations on extinction rates is a central question in conservation biology, ecology, and evolution. We show that the effect of subdivision on the mean time to extinction in independently varying habitat patches depends upon the relationship between extinction probabilities and habitat area Models of extinction by demographic stochasticity alone predict that subdivision should decrease the mean time to extinction. If environmental stochasticity is incorporated into the model, subdivision may increase the mean time to extinction. Empirical species persistence times estimated from island bio‐geography studies show no systematic relationship to the degree of subdivision. However, subdivision always increases the probability of survival over a sufficiently short time interval. These results suggest that over ecologically relevant timescales, subdivision into a number of independent sub‐populations may frequently act to decrease the probability of overall extinction in rare species. To the degree that these considerations may be applied to rare and endangered species, maintaining sufficient numbers of nature reserves is likely to be crucial to effective conservation strategies.